Surprisingly high network traffic between kafka servers

Hello,

I'm running a 0.8.0 Kafka cluster of 3 servers. The service that it is
for is not in full production yet, so the data written to cluster is
minimal (seems to average between 100kb/s -> 300kb/s per server). I
have configured Kafka to have a 3 replicas. I am noticing that each
Kafka server is talking to all the others at a data rate of 40MB/s for
each server (so, a total of 80MB/s for each server). This
communication is constant.

Is this normal? This seems like very strange behavior and I'm not
exactly sure how to debug.

Thanks,
Carl